Thermostatic switch



S. MARVIN June 10, 1941.

THERMOSTATI C SWITCH Filed Sept. 16, 1938 I l l I l I I l I I I I I I I l |L m ll w X mkivnm v 1 N VEN TOR.

STA NL 57 MARVIN BY J A ORNEY.

Patented June 10, 1941 2,244,915 THEBMOSTATIC swri'cn Stanley Marvin, Burlingame, Calif., assignor to B. E. wltkin, olkllndycalif.

Application September 18, 1938, Serial No. 230,300

Claims.

This invention relates to thermostatic control for electrically heated devices generally, and in particular to electric flat irons, though the invention is applicable to anyelectrically heated device for automatically controlling the temperature of the device.

The principal object of "the invention is to provide a simple strip thermostat of homogeneous metal which will be sensitive, fast acting, and relatively powerful for any given size. Other features and advantages of the invention will appear in the following description and accompanying drawing.

In the drawing:

Figure 1 is a side elevation of an electric fiat iron with portion broken away and shown in vertical section to show the application of my improved thermostatic control thereto.

Figure 2 is a detached plan view of the heat responsive element and its adjustable anchor plate.

er side of the thermostat adjusting cam. Fig

ure 8 is a fragmentary sectional elevation of the body of the iron showing a modified form of thermostat in place.

In further detail, the electric iron comprises a cast base portion I. a hollow body portion 2, a hollow handle portion 3 preferably of composition material to reduce heat transfer, and 4 an electric heating coil of flat form positioned in a, slot formed in.the base and from which element at least one of its lead wires 5 extends to a snap switch generally designated A for cutting off the current at determinable temperature rises through means of the thermostat shown detached in plan in Figure 2.

The thermostat comprises a pair of overlying elongated upper and lower strips 8 and II of sheet metal, with a shorter piece 9 of sheet metal angularly positioned between strips Sand II and secured at its ends respectively to the overlapping ends of strips 8 and ii as by rivets 8, welding, or by other integral connection as by folding back from strip II as shown at ill, or any other desired way so as to form of piece 9 a tiltable strut adapted to tilt when strips 6 and II are pulled in opposite directions, to thereby force the strips apart. Upper strip 6 is fill anchored at its extreme left end only as by one or more rivets or screws I to the body or other rigid portion of the fiat iron as indicated, while the extreme right end of lower strip II is extended beyond the rivets 8 and ,pivotally riveted or screwed as at I! to a cross bar or anchor plate II itself pivoted at ll to the body of the iron or other fixed support, and with its opposite end ll' free for arcuate adjustment on its pivot by means of a screw l5 threadedly engaging an upturned lug It on the cross bar.

The short leg 9 or tiltalble strut portion of the thermostat, or the upper strip 6, is extended beyond rivets I and bent upwardly to form a small elevated step ll arranged in proximity to a small push button It protruding from the 7 lower wall of the snap switch A, all so that as the thermostat is deflected upward step portion i-l will push this button in, and upon movement downward will permit it to snap out again.

The thermostat or heat responsive element above described will be seen to be three connected strips 6, 9, ll, of flat metal taking the form of a narrow letter N, but with the two outer strips or legs much longer than the angular leg or strut, and both outer legs anchored at their. outer ends (one of them being adjustably anchored) and connected at their inner overlapping ends to opposite ends of the angular leg or strut so as to tilt, the same when the outer legs or strips are pulled in opposite directions. The device is preferably made of a good grade of steel, clock spring quality having been found very satisfactory, and though shown as made with a joint at 8, may if. desired be bent out of a single piece to the form shown, and portion ll welded to it, or omitted entirely and the ad- Jacent. portion arranged to operate the push button of the snap switch. If clock spring metal is used, its temper should be drawn to form it and restored afterward.

It should be noted that the portion at It where the short leg 9 joins the lower leg II, is supported against downward deflection by a ledge I! of the body or other rigid portion of the iron..

The action of this thermostat is that since both extreme ends of the steel strip are anchored, a'ny outward movement of the two long legs of the strip, or either leg, will tend to tip the angular .leg 9 to a greater angle and thus raise the free end l1 and push the switch buttons, as the lower leg is supported against down ward deflection at l9.

The body or base ofthe electric iron" to which the opposite ends of the steel strip are anchored is made of aluminum or aluminum alloy oi considerably greater expansive value under heat than the steel, and hence the more rapid elongation of the body pulls the lower and upper runs of the N-shaped strip away from one another and thereby causes the angular leg to rapidly force the upper leg 6 upwardly as the heat increases.

Another feature which increases the effect is that the steel stripe, '9, H, has but little direct contact with the body of the iron and would normally be somewhat cooler than the body and base of the iron, particularly as it is relatively remotely situated from the electric heating element.

In order to predetermine the tension on the steel strip at any given heat, anchor lever i3 may be moved slightly to the right by screw ii to increase the tension or slalcked off to reduce the tension. This would be considered a factory adjustment to compensate for possible discrepancies in manufacture of the parts and locating of the anchoring rivets or screws, but to provide for easy adjustment of the thermostat to operate the switch at various temperatures 1 provide means for applying Pressure upon the upper leg 6 at a point intermediate its length. This means is shown in the drawing as a disk 23 overlying leg 8 and formed with a circular hub 2i revolvably positioned in a circular hole in a plate 22 which covers the thermostat assembly and the depression 23 in the body of the iron in which it is located, and which disk has a cam rim 24 formed on the edge of its lower side adapted to bear upon the upper side of leg 8 to force it down more or less as'the disk is turned, and at the end of the cam rim is an abrupt lug 28 which will strike the edge of the leg and thus limit the turning of the disk in both directions.

To turn the disk I provide a handle or knob 28 secured to the disk as by a countersunk screw 21, and the knob is of wing nut form with flat wings 23 or other well defined portion adapted to cooperate with marks or raised indicia 2! formed on the top of plate 22 to indicate the adjustment to be for medium, hot, or very hot, as may be desired. .To insure rigid connection of the knob and disk, and also the proper positioning of the knob with proper relation to the cam surface, I provide two different size pins 3|, 3|, which proiect upwardly from the disk into complementarily formed holes in the lower side of the knob; or just one pin and one hole could be-used for the same purpose.

. Figure shows the relation of the cam rim of the disk to the leg 8 when viewed from beneath, and will clarify the above description.

Snap switch A may be of any suitable type which is normally closed and will snap on upon slight pressure and snap on again when the pressure is released. A standard article obtainable on the market, however, is known as the "Micro switch and is the one here shown, and its operating button ll need be depressed but a small fraction of an inch (about 6 inch or less) and the circuit contacts will be instantly separated with a snap action, and upon release of the button will snap closed again.

Since this switch is a self-contained unit well known in the trade, detailed description would seem superfluous, but it will be generally described to complete the specification. The-elements of the switch are enclosed in a heat resisting and electric insulating case 32 having a cover or removable side 33 through which a small push button i8 slidably projects. The inner end of the crumed at their ends at 3!- almost in plane with the central tongue. The outer end of the central tongue is anchored at 38 to a hollow terminal bolt 39 to which one of the circuit wires 40 is secured, and the opposite end of the spring group carries a contact element II which is normally pressed by the springs against a contact plate 42 anchored to another terminal bolt 43 to which the other wire 5 of the circuit is secured. Figures 3 and 4 show the construction clearly, Figure 4 being a bottom plan view with the cover 33 omitted.

The snap switch unit is suitably secured in place on the iron as by one or more bolts ll clamping'it to a suitable bracket 45 firmly secured to the body of the iron as at 46.

The handle 3 of the iron is a hollow shell suitably secured to the iron as by bolts I1, and it forms a housing over the switch and circuit wiring connections as shown. The handle is also preferably vertically split longitudinally and its halves held together as by screws 43 so that the switch and connections will be accessible upon removing one side of the handle.

Suitable electric leads extend from the switch and heating element to an outside source of electric current, but as such connections are well understood are not detailed in the drawing.

In considering the invention as above set forth it will be seen that the action of my thermostat does not depend on the expansive effect of the steel strip but rather on the expansion of the body or base of the iron, and which, if of aluminum or alloy, is considerable and hence the steel strip could be replaced with a strip of Bakelite, or any substance able to resist the heat normally used in an electric iron, as the less expansion it had the better its action, but it should be resilient in order to recover after deforming by cam 24 to avoid the use of a spring to push it back.

Also to be noted is that the action of the short angular leg I is merely that of a mechanical strut 'in forcing the two outer-legs apart, andbence instead of being riveted at its ends to the other legs or formed integral with them, it could just as well be pivoted to them, but it operates satisfactorily without this extra work.

Also, it will be seen from the above description that while I show two strips arranged to pull 0pposite ends of the angular strut in opposite directions to force the overlapp ng ends of the strips apart, or rather force the per one upwardly twice the distance it would normally go, as the lower one is blocked against downward movement, yet the device would operate with but one of the strips; thus, it the lower strip were omitted and the left hand end of the strut 8 were blocked against slipping along the support is, the elongation of the body 2 relative to the upper strip 6 would tilt the strut, but. of course only about half as much as though both strips were used.

Also, since the strut'merely functions as means for quickly forcing the strips apart as the supporting body to which they are secured elongates, one or more wedge blocks could be substituted for the strut as shown in Figure 6 wherein the upper and lower strips are designated 6' and H and each has a wedge block 49-50 secured to its overlapping end and so arranged that a pulling of the strips outwardly, as by expanding the 1 base I, will at once force the upper strip upwardly to operate the switch button it.

It will be evident from the above description and showing in the drawing that minor changes in the construction may be resorted to at numerous points without altering the mode of operation, and any such changes are intended to be included in my appended claims.

I claim:

1. In a thermostat, a tiltable strut, a heat expansive body, elongated strips extending in opposite directions respectively connecting opposite ends of said strut with remote points on said body in a manner to cause tilting of said strut upon the pulling of said strips through elongation of said body upon expansionby heat, and switch means operated by the tilting of said strut.

2. In a thermostat, a tiltable strut, a heat expansive body, elongated strips extending in opposite directions respectively connecting opposite ends of said strut with remote points on said body in a manner to cause tilting of said strut upon the pulling of said strips through elonga tion of said body upon expansion by heat, and a spring actuated snap switch operated by the tilting oi said strut, said switch being adapted to snap to reverse position upon reverse movement r said strut.

3. In a thermostat, a tiltable strut, a heat expansive body, strips extending inopposite directions along opposite sides of and in overlapping relation to said strut and respectively connecting opposite ends of said strut with remote points on said body in a manner to cause tilting of said strut upon opposite directional pulling of said strips by elongation of said body upon expansion by heat, and switch means operated by the tilting of said'strut, the connection of one of said strips to said body comprising a shiftable anchor, and means for adjusting the position of said anchor to vary the tensional pull in said strips.

4. In a thermostat, a tiltable strut, a heat expansive body, strips extending in opposite directions along opposite sides of and in overlapping relation to said strut and respectively connecting opposite ends of said strut with remote points on said body in a manner to cause tilting of said strut upon opposite directional pulling or said strips by elongation of said body upon expansion by heat, and switch means operated by the tilting of said strut, the connection or one of said strips to said body comprising a lever pivoted to said strip and the lever in turn pivoted to said body, and means for adjusting the position of thelevertovarythetensionalpullinsaidstrips.

5. In a thermostat, an electrically heated body adapted to elongate by heat, a pair of elongated strips secured to remote points to said body and extending toward one another with ends in overlapping relation, means between and cooperating with the overlapping adjacent ends of the strips arranged to force them apart laterally when the strips are pulled relatively in opposite directions, and an electrical switch operated by the lateral movement of said strips relatively.

6. In a thermostat, an electrically heated body adapted to elongate by heat, a pair of strips secured to remote points to said body and extending toward one another in overlapping relation at their ends only, an electrical snap switch, and means between and operated by said overlapping ends for operating said switch by relative movement of said strips when pulled by elongation of said body, said strips being of a lower heat expansive value than said body.

- first strip, an angularly arranged strut between the overlapping ends of the strips connected at its ends respectively to said strips in a manner to tilt and force their overlapping ends apart when the strips are pulled relatively in opposite directions, and one of the overlapping ends being supported by said body against outward movement, so as to limit all outward movement to the other, and a switch element operated by movement of the free strip and strut upon elongation of said body upon expansion by heat.

,8. In the construction set out in claim 7, manually adjustable means for more or less deflecting said elongated strip at an intermediate point.

9. In the construction set out in claim 7, manually atfiustable means for varying the tensional pull in the two strips.

10. In a thermostat, means for developing motion for operating a switch, comprising an elongated strip, a tiltable strut extending along said strip and arranged upon tilting to deflect said strip to operate said switch, said strip connected at one end only to said strut adjacent one end of the strip, a fulcrum supporting the opposite end of said strut, and heat expansive means arranged upon expansion for pulling the opposite end of said strip to thereby tilt said strut, and manually operated means for deforming said strip at a point intermediate its length to vary its etfectiveness in tilting said strut.

STANLEY MARVIN. 

